Amateur lathe user requesting assistance

Analog · Nov 7, 2021

Hello everyone!

I am an amateur garage "machinist" looking for advice. I am using an expanding lathe to turn these polymer washers. I am turning about 40 washers on the expanding mandrel shown.

I am looking for a lathe tool with a wide cutting edge to trim the washers down to a consistent size. I am using a starter set of lathe tools which are very narrow, and I tend to get uneven results on the outside diameter as I work sideways across the OD. Sometimes +/- 1-2mm. I can turn the lathe tool sideways to achieve a uniform finish, but that is dangerous and the tool isn't particularly sharp on its edge.

If someone could recommend a tool for this application and a place to buy it and I'd really appreciate it. Thanks for your time

Joe Gwinn · Nov 7, 2021

That appears to be a woodworking lathe of some sort. This is a metalworking group.

You may have better luck asking at rec.woodworking or the like.

Analog · Nov 7, 2021

Joe Gwinn said:
That appears to be a woodworking lathe of some sort. This is a metalworking group.

You may have better luck asking at rec.woodworking or the like.

Thank you for the suggestion. I apologize for my noob-iness, I just didn't know where else to ask.

L Vanice · Nov 7, 2021

A skilled woodworker can produce a fairly accurate cylinder on a wood lathe with hand-held chisels. It takes practice and experience or really good instincts.

There are some special devices made to take some of the skill out of the work. These duplicator attachments are usually made to hold an irregular shaped template that the cutting tool is forced to follow. They are good for making matched sets of table and chair legs, for instance. The template can simply be a straight edge and, once set in the right position, it will produce a straight cylinder.

Lathe Duplicator attachments at Penn State Industries

A T-rest with a straight edge facing the operator and a gouge with an adjustable stop collar would be a very simple way to generate a cylinder.

In a metalworking shop, almost any common metal lathe will easily produce an accurate cylinder shape with very little skill needed.

Larry

Illinoyance · Nov 7, 2021

Use a gouge. Put a collar on the gouge that bears against the back of the tool rest. That will hold a consistent diameter as long as the tool rest is parallel with the spindle.

rke[pler · Nov 7, 2021

I would have some suspicion that the taper arbor might not be the right place to mount the washers. It might be better to make a fixed diameter arbor that would clamp all the washers together and eliminate some of the wibbly-wobbly that you're going to see near the ends.

Another thing you might do is to cool the whole assembly down. A cooler polymer is a stiffer polymer and a lot easier to cut cleanly.

L Vanice · Nov 7, 2021

rke[pler said:
I would have some suspicion that the taper arbor might not be the right place to mount the washers. It might be better to make a fixed diameter arbor that would clamp all the washers together and eliminate some of the wibbly-wobbly that you're going to see near the ends.

Another thing you might do is to cool the whole assembly down. A cooler polymer is a stiffer polymer and a lot easier to cut cleanly.

OP did say, "I am turning about 40 washers on the expanding mandrel shown." The tapered part causes the split sleeve to expand, so the washers are not sitting on a taper. The mandrel might have cost more than his lathe, judging by what my KO Lee and German expanding mandrels cost.

Larry

rons · Nov 7, 2021

All you need is one or two fingers as a guide on that tool rest and a light cut. This is easy if the tool rest has a straight edge on the back side.
A tool rest with a raised lip is what I mean. I run a finger on the back of the raised edge in the front tool rest. Can you take a picture of the
tool rest with the scraping tool removed?

With what you already have there a back and forth stroke would hit on a few rings. Then you keep going until the array of washers is flat.
Looks like you are scraping. Try shear scraping with a narrow gouge not a wide flat scraper. It works because I did this stuff before with a woodworking lathe.

If your speed is too high a cut on washer is going to heat up adjacent washers and the material will swell a bit and get out of shape.
With a wide scraper like that I think you are trying to take too much off at one time.

Another thing you can do is attach metal washers at both ends with identical diameters (internal and external). They will act as depth stops.

michiganbuck · Nov 7, 2021

if the holes are close to the same size it may be better to use a shoulder and nut mandrel.

rons · Nov 7, 2021

You can mount a square bar (1/2" x 1/2") on the tool rest and rig up a narrow gouge with an adjustable collar secured by a allen screw.
The collar can only go as far as the square bar and stop your gouge from getting pulled into the plastic.

partsproduction · Nov 7, 2021

Long I ago surmised that a rotary knife would be the ticket for turning rubber, and years later watched a tire peeler (Not sure what they are called) use that same idea. Perhaps a die grinder with about a 1 or 2" diameter circular knife would work but I for one would never use it if held only by hand. Liquid soap would help diminish the friction the contact with the rubber would cause.
Of course the OP described the washers as "Polymer", which can mean a huge number of materials, I prefer the word plastic, but some polymers have characteristics very much like rubber.

rke[pler · Nov 8, 2021

L Vanice said:
OP did say, "I am turning about 40 washers on the expanding mandrel shown." The tapered part causes the split sleeve to expand, so the washers are not sitting on a taper. The mandrel might have cost more than his lathe, judging by what my KO Lee and German expanding mandrels cost.

Larry

Yeah, I had a brain fart and said "taper arbor" instead of "expanding arbor". But the point is that you want the material held as rigidly as possible under the cutter so that the pressure of the cutter cuts rather than bends the material. This also suggests positive rake tooling going to knife-edge cutters when you can. I have also heard of folks using toolpost grinders to machine rubber rollers, maybe in conjunction with chilling the roller.

FredC · Nov 8, 2021

Would like to ask the OP how many, continuous need or just one batch? How hard is the plastic. The attached photo shows an old Atlas lathe modified with a light duty CNC slide. We used to turn and chamfer thousands of Laser cut acrylic disks in 2 different diameters. Job went away and this thing has not been used in 20 years. Would not be hard to modify it to do washers. The tail stock wheel was replaced with a weight that trapped the disks between a the driver in the head stock and the pressure flat in the tail stock. took a second to load a few seconds to do a couple passes to finish the disk.

cg285 · Nov 8, 2021

partsproduction said:
Long I ago surmised that a rotary knife would be the ticket for turning rubber, and years later watched a tire peeler (Not sure what they are called) use that same idea. Perhaps a die grinder with about a 1 or 2" diameter circular knife would work but I for one would never use it if held only by hand. Liquid soap would help diminish the friction the contact with the rubber would cause.
Of course the OP described the washers as "Polymer", which can mean a huge number of materials, I prefer the word plastic, but some polymers have characteristics very much like rubber.

i guess at times i am a tire peeler. wish i had thought of that name
my machine has a round blade spinning against a tire spinning. never saw anything different

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